The dynamical hole in ultrafast photoassociation: analysis of the compression effect

TL;DR

This paper analyzes how short chirped laser pulses create a dynamical hole in the wavefunction during ultrafast photoassociation, leading to a compression effect that enhances atom pair density at short distances and influences vibrational populations.

Contribution

It introduces a detailed analysis of the dynamical hole and compression effect in ultrafast photoassociation, with a focus on optimizing parameters to increase short-range atom pair density.

Findings

Over two orders of magnitude increase in short-range density probability.

Prediction of enhanced photoassociation rates into deeply bound levels.

Identification of parameter regimes for optimal compression effect.

Abstract

Photoassociation of a pair of cooled atoms by excitation with a short chirped laser pulse creates a dynamical hole in the initial continuum wavefunction. This hole is manifested by a void in the pair wavefunction and a momentum kick. Photoassociation into loosely bound levels of the external well in Cs_2 0$_g^-$(6S + 6P$_{3/2}$ is considered as a case study. After the pulse, the free evolution of the ground triplet state wavepacket is analyzed. Due to a negative momentum kick, motion to small distances is manifested and a compression effect is pointed out, markedly increasing the density of atom pairs at short distance. A consequence of the hole is the redistribution of the vibrational population in the ground triplet state, with population of the last bound level and creation of pairs of hot atoms. The physical interpretation makes use of the time dependence of the probability current and population on each channel to understand the role of the parameters of the photoassociation pulse. By varying such parameters, optimization of the compression effect in the ground state wavepacket is demonstrated. Due to an increase of the short range density probability by more than two orders of magnitude, we predict important photoassociation rates into deeply bound levels of the excited state by a second pulse, red-detuned relative to the first one and conveniently delayed.